Current experiments seek to study (1) the regulatory significance of the alternative forms of ribonucleotide reductase; (2) validity of the "methylfolate trap" theory on vitamin B12 action; (3) levels of "methyltransferase" and other enzymes catalyzing interconversions of folate compounds in normal and leukemic blood cells; and (4) studies of the synthesis and degradation of pteroylpolyglutamates in animal cells. BIBLIOGRAPHIC REFERENCES: Thorndike, J., and Beck, W.S., Production of formaldehyde from N5-methyl-tetrahydrofolate by normal and leukemic leukocytes. Cancer Res. 37: 1125-1132, 1977. Beck, W.S., Hematology, 2nd edition, The MIT Press, Cambridge, 1977.